Semiconductor device fabrication technology has entered the ultra-large scale integration (ULSI) domain with submicron sized device structures. This increased level of integration has significantly improved the switching speeds of the integrated circuits; however, full utilization of the faster integrated circuits in configuring high-performance systems requires a comparable advance in the technology used to interconnect the device structures. At present, interconnection technology has clearly emerged as the performance limiting factor in high speed systems. Prior methods of interconnection have suffered from the inability to satisfactorily address issues in addition to speed, such as power dissipation, cross-talk, and fan-out. All of the issues must be addressed in order to take full advantage of the ultra-large scale integration technology.
Transmission of optical signals through optical waveguides has found application in such fields as telecommunications, biomedical monitoring systems and other analytical applications. Prior attempts to extend this technology to the microelectronic industry have produced less than satisfactory results. One drawback has been the inability to obtain a high enough difference in the index of refraction of the waveguides and the index of refraction of the surrounding medium. Without a large enough difference, leakage of signals from the waveguides can rise to unsatisfactory levels. Signal leakage is undesirable because of the potential for cross-talk between adjacent waveguides. Although the degree of cross-talk can be reduced by spacing the waveguides a sufficient distance apart, such a remedy is generally unsatisfactory in applications where dense packing of components is a requirement. Another drawback was inadequate thermal stability of the waveguides when subjected to normal processing conditions.
The developing multi-chip module packaging technology promises higher connectivity, faster electrical performance, more efficient thermal management and better reliability. Dielectric materials, such as polyimide, with its low dielectric constant and superior planarization characteristics, is playing a key role in the metal/polyimide hybrid wafer scale integration technology. Nonplanar ridge waveguides have been used as pathways for guiding electromagnetic waves in polyimides. While suitable for some purposes, these ridge-type waveguides with their vertical profile are not suitable for use in technology, such as multi-chip module packaging, which requires a planar structure so that multiple layers of elements or components can be stacked on top of one another.
Any newly developed connection system should be compatible with other elements in the integrated circuit and should not adversely impact their function. The connection should efficiently transmit signals without losses that will result in unsatisfactory performance of the integrated circuit.
The low-loss channel waveguides formed in accordance with the present invention provide a solution to the problems which heretofore have remained unsolved.